Method for producing cement

ABSTRACT

A method for producing cement useful for preparing pastes, mortars, concretes and other cement-based materials, having a high workability with reduced water content, high strength and density, and a rapid development of strength, which method includes a mechanicochemical treatment of cement. The method includes a two-stage mechanicochemical treatment of a mixture of cement and at least one of two components, the first component being a SiO 2  -containing microfiller and the second component being a polymer in the form of a powdery water-reducing agent. In the first stage the cement and the first and/or the second component are intensively mixed in a dry state, whereby particles of the first and/or the second component are adsorbed on the cement particles. In the second stage the mixture obtained in the first stage is treated in milling equipment where the particles in the mixture receive in quick succession a large number of direct-changed impact impulses resulting in modification of the surface properties of the cement particles in the form of substantial increase of surface energy and chemical reactivity. The treatment in the second stage is carried out during a sufficiently long period of time in order that a 1-day compressive strength of a 20 millimeter per side cube of cement paste, which has been properly compacted under vibration and hardened at +20° C. in sealed conditions, at least equals 60 MPa.

This application is a 371 of PCT/SE94/00389, filed Apr. 29, 1994.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of producing cement useful forpreparing pastes, mortars, concretes and other cement-based materialswith high workability at low water content, high strength and strengthdevelopment and high density. The method includes mechanicochemicaltreatment of a mineral-polymeric or a mineral mixture of portland cementand a SiO₂ -containing microfiller, for example silica fume, and/orpowdery water reducing agents of melamine or naphthalene type in millingequipment, preferably with vibration grinding media.

2. Description of the Related Art

The prior art closest to the method according to the present inventionis a method described in an article in Journal Concrete International,October 1992, page 56 with the title "Intermilled Silica Fume inIcelandic Cement" and the method described in the patent GB 2,006,737for a "Method and apparatus for production of an activated mineralcomposition."

The first mentioned method (Concrete International, 1992 "IntermilledSilica Fume in Icelandic Cement") discloses milling of a cement clinkerwith gypsum and other additives together with silica fume. The lastcomponent is added in an amount of 5-7.5% by weight of clinker. By saidmethod one tried to achieve a higher level of homogenization of theblended cement in order to obtain a more stable concrete with highmechanical properties. This method does not include the use of apolymeric component (e.g. powdery water reducing agents). There is nodisclosure of any substantial increase of the strength development andof the density of the hardened cement paste or concrete. This is thecase because due to high hardness and density of the rather coarsecement clinker particles, practically all the energy of the grindingmedia is used to crush the material without any significant increase ofthe surface energy of treated cement and consequently there is noincrease of the strength development and ultimate strength of cementpastes, mortars and concretes.

The second mentioned method according to GB 2,006,737 suggests wellknown conventional mechanical grinding and activation of fine-grainedcement mortar, which consists of ordinary portland cement with anaverage particle size of about 10 μm and fine sand with a particle sizeof 60-1000 μm (0.06-1.00 mm) in a pinned disk mill or vibration mill.

Due to the nature of mineral mixture components, particle sizedistribution and parameters of treatment, disclosed by this method, themain part of the consumed energy is used for decreasing the particlesize of sand and cement and only a small part of it is stored as surfaceenergy. There are also no basic changes and/or modifications of thematerial microstructure and main properties of the substance. This caneasily be illustrated by the relatively low values of ultimatecompressive strength of the mortar obtained with this activated cement,namely 55-65 MPa after 28 days of hardening, and also by a rather shortperiod of strength development, as the hydration of the "activated"cement is almost stopped after 7 days of hardening.

Due to the relatively low level of stored surface energy and due to itsrelaxation, the cement particles start to lose their obtained propertiesafter 2-3 weeks of storage.

Another serious drawback of this method is a drastic increase of thesurface area, which according to generally approved knowledge leads to arequired increased amount of water in a concrete mixture, i.e. the waterto cement ratio, required to maintain workability (plasticity).According to this known method, the water to cement ratio is ratherhigh, about 0.6. This fact is negative from the point of view ofincreased porosity, increased shrinkage, limited level of strength andlow durability.

SUMMARY OF THE INVENTION

The present invention relates to a method for producing cement usefulfor preparing pastes, mortars, concretes and other cement-basedmaterials, having a high workability with reduced water content, highstrength and density and a rapid development of strength. The methodincludes a two-stage mechanical treatment of a mixture of cement and atleast one of two additional components. The first component includes anSiO₂ containing microfiller and the second component includes a polymerin the form of a powdery water reducing agent. In a first stage thecement and said first and/or said second component are intensively mixedin a dry state, whereby particles of the first and/or the secondcomponent are adsorbed on the cement particles. In a second stage themixture obtained in said first stage is treated in milling equipmentwhere the particles in said mixture receive in a quick succession alarge number of direct-changed impact impulses resulting in modificationof the surface properties of the cement particles in the form of asubstantial increase of surface energy and chemical reactivity. Thetreatment in said second stage is carried out during a sufficiently longperiod of time in order that a 1-day compressive strength of a 20millimeter per side cube of cement paste, which has been properlycompacted under vibration and hardened at +20° C. in sealed conditions,at least equals 60 MPa.

Further, the invention relates to a process for preparing a shapedconcrete element or structure which includes the steps of firstlyproducing a cement according to the above said method and secondlymixing said cement with sand and/or aggregates of greater dimensions andwater, and thirdly casting a shaped element or structure and hardeningof the subject.

Still further, the invention relates to the use of cement produced bythe method described above as an additive to a cement, such as ordinaryportland cement, as an accelerator of the hardening process of suchmixture.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail in the followingdescription, partly in connection with Tables and Figures, wherein

FIG. 1 is a diagram showing strength development at 20° C. curing forcement paste. In FIG. 1 the curve marked 1 refers to cement according tothe present invention, the curve marked 2 refers to cement+5% silicafume according to prior art and the curve marked 3 refers to cementaccording to the prior art.

FIGS. 2a and 2b respectively are diagrams showing strength developmentof concretes cured at 20° C. In FIGS. 2a and 2b EM(An1) stands forconcrete with the cement according to the present invention. An1 standsfor concrete according to the prior art.

FIG. 3 is a diagram showing compressive strength as a function oftemperature-equivalent time. In FIG. 3 EMC(An1) stands for concreteaccording to the present invention. An1 stands for concrete according tothe prior art.

FIGS. 4a and 4b respectively are diagrams showing strength developmentfor concrete with a binder content of 480 kg/m³ cured at negativetemperatures with the antifreezing admixture "BETEC". EM(An1) stands forconcrete according to the present invention. An1 stands for concreteaccording to prior art.

FIG. 5 is a diagram showing liberated heat as a function oftemperature-equivalent time. EMC(An1) stands for concrete according tothe present invention. An1 stands for Concrete according to the priorart.

FIG. 6 is a diagram showing liberated heat per strength unit as afunction of temperature-equivalent time. EMC(An1) stands for concreteaccording to the present invention. An1 stands for concrete according tothe prior art.

FIG. 7 is a diagram showing pore size distribution. In FIG. 7 the curvemarked 1 refers to cement paste according to the prior art, the curvemarked 2 refers to cement paste with 10% silica fume according to theprior art and the curve marked 3 refers to cement paste according to thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

It has now been found that when treating a combined mineral-polymeric ormineral mixture of portland cement and SiO₂ -containing microfiller,preferably silica fume and/or polymer in the form of powderywater-reducing agent together with media milling equipment (e.g.stirred, centrifugal, tumbling ball) or non-media milling equipment(e.g. jet, impact, roller), preferably in mills with cylbeps' vibrationgrinding media much more improved mechanicochemical activation of thecement takes place. This treatment also leads to the basic changes andmodification of the material microstructure and its properties. Duringthe mechanicochemical treatment according to the present inventionseveral processes take place simultaneously.

Firstly, every particle of the portland cement, microfiller and/orpowdery reducing agent receives a large number of direct-changing,randomly distributed impact impulses in a quick succession from thegrinding media and other elements of the milling equipment. During thistreatment finer and lighter particles of the microfiller (silica fume)and/or the powdery water-reducing agent build up a cover around thecement particles. This cover then acts as lubrication between the cementparticles and the grinding media.

Secondly, the newly formed cover of silica fume and/or powderywater-reducing agent particles transforms the impact impulses of thegrinding media and all the potential and kinetic energy of the grindingmedia and other elements of the milling equipment (e.g. stators, rotorsand etc.) to create mainly shape deformations and microdefects of thecement particle surfaces.

The present process drastically increases the surface energy andchemical reactivity of the cement particles. Besides, due to theabsorption of silica fume and/or powdery water-reducing agent theparticles will obtain an electrostatic charge and are attracted to eachother promoting consolidation and agglomeration of the particles, whichwill prevent any substantial increase of the cement paste water demand.

Thus, due to the mechanicochemical treatment according to the presentinvention a discontinuous network of the new modified binder material onthe surface of the cement grains and microdefects inside the surface ofthe cement grains are created. This new binder has an extremely highchemical reactivity and high hydrophobic properties (mainly in the caseof use of a powdery water-reducing) agent. In our opinion the layers ofthis new binder have a very high potential of nucleigeneration andimproves the hydration process especially in the early age period of thehardening process, where the compressive strength of the cement pastesand concretes with the cement obtained according to the presentinvention is up to 300% higher than the conventional reference pastesand concretes.

Furthermore, this new binder creates and maintains the metastability ofthe system and this gives a possibility for cements, produced accordingto our present invention, to hydrate in a more prolonged period of timeand to reach a higher rate of strength development.

At this moment we cannot provide a full theoretical explanation of thephenomena, but the description mentioned above gives, according to ouropinion, a basic phenomenological picture of the process according tothe present invention.

The cement produced according to the present invention has surprisingproperties, which have no analogs in modern technology today. Thiscomplex of properties cannot be obtained by any other known method.

The properties of the material treated according to the presentinvention can be listed as follows:

the cement produced according to present invention keeps all propertiesas commercially produced (portland) cement during a rather long periodof storage (more than 9 months) according to the requirements ofbuilding practice;

up to 50% decrease of water demand is obtained in comparison withordinary cement with preservation and even improvement of the level ofconsistency of the cement paste and workability of the concrete mixture,see tables 1 and 2, which leads to a creation of a more dense structureand a high strength of the material.

Table 1 refers to influence of the present method on the consistency ofcement paste.

Table 2 refers to influence of the present method on the workability ofa concrete mixture.

                  TABLE 1                                                         ______________________________________                                        influence of the method of cement treatment on the normal                     consistency of the cement paste.                                                                               Normal                                                                        consistency,                                                   Composition of water % to                                   No   Type of cement                                                                             binder         binder weight                                ______________________________________                                        1    Binder treated                                                                             Portland cement =                                                                          94% 15,0%                                           according to silica fume =                                                                              5%                                                  the present  powdery water =                                                                            1%                                                  invention    reducing agent                                                                ("MIGHTY 100")                                              2    Ordinary portland                                                                          Portland cement                                                                           100% 28,3%                                           cement                                                                   3    Binder treated                                                                             Portland cement =                                                                          94% 23,8%                                           according    silica fume =                                                                              5%                                                  to prior art Powdery water- =                                                                           1%                                                  method       reducing agent                                                                ("MIGHTY 100")                                              ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        influence of the method of cement treatment on the workability                of the concrete mixture.                                                                                   Water to                                                                              Workability                                                Cement content                                                                           cement ratio                                                                          slump                                    No   Type of cement                                                                             kg/m3      W/C     mm                                       ______________________________________                                        1    Cement treated                                                                             480        0,21     47                                           according to                                                                  present invention                                                        2    Cement treated                                                                             480        0,27    150                                           according to                                                                  present invention                                                        3    Cement treated                                                                             340        0,35    100                                           according to                                                                  present invention                                                        4    Cement treated                                                                             270        0,46    105                                           according to                                                                  present invention                                                        5    Cement treated acc.                                                                        480        0,21    No slump C                                    to prior art method                                                                        480        0,27     50                                      6    Cement treated acc.                                                                        340        0,35    No slump C                                    to prior art method                                                                        340        0,56     92                                      7    Cement treated acc.                                                                        270        0,70    100                                           to prior art method                                                      ______________________________________                                    

the rate of the strength development of the cement paste and concrete isdrastically increased in a wide range of positive curing temperatures,namely from +5° to +50° C., see FIGS. 1, 2 and 3. More intensivehardening of concrete also takes place at negative temperatures, namelyat -10° C. and -20 C. when used with an antifreezing admixture, see FIG.4. The properties mentioned above provide the reduction of form removaltime, gives a lower risk to easy freezing, a substantial decrease of thebuilding process and a simplification of winter concreting operations.

concretes produced with the use of cement manufactured according to thepresent invention have approximately the same resulting heat ofhydration per cement weight with a slightly higher rate of heatliberation in comparison with concretes prepared by the prior artmethod, see FIG. 5. At the same time concretes produced with the cementaccording to the present invention have significantly lower heatproduction per strength unit than concretes prepared by the prior artmethod, see FIG. 6. This reduces the probability of thermocracking.

porosity of the cement paste is reduced to less than half compared withprior art methods, see FIG. 7. The concrete becomes practicallyimpermeable and durable;

intensive self-desiccation of the concrete takes place together withstrength increase at the early age of hardening. The values of therelative humidity are approximately 72-74% already after ten days ofcuring in sealed conditions and at room temperature.

As stated above, the method according to the invention includes atwo-stage mechanicochemical treatment of a mixture of cement and atleast one of two additional components, the first component being a SiO₂containing microfiller and the second component being a polymer in theform of a powdery water-reducing agent.

This means that the invention covers three different cases, namely afirst case where cement and both the first and the second components aremixed, a second case where the cement is only mixed with the secondcomponent and a third case where the cement is only mixed with the firstcomponent.

Certainly, the compressive strength will vary depending on whatcomposition the mixture has according to said three different cases.

Further, it is stated above that said treatment, according to the secondstage of the method, is carried out during a sufficiently long period oftime in order that a 1-day compressive strength of a 20 millimeter perside cube of cement paste, which has been properly compacted undervibration and hardened at +20° C. in sealed conditions, at least equals60 MPa.

According to a preferred embodiment said treatment is carried out duringa period of time such that said compressive strength is at least 70 MPa,in the case of a mineral-polymeric mixture comprising 94% of ordinaryportland cement, 5% of silica fume and 1% of a powdery water reducingagent named "MIGHTY 100", and in addition 16% of water by the weight ofthe solid components.

According to another preferred embodiment said treatment is carried outduring a period of time such that said compressive strength is at least65 MPa, in the case of a mineral-polymeric mixture comprising 99.0% ofordinary portland cement, 1% of a powdery water reducing agent namedMIGHTY 100, and in addition 16% of water by the weight of the solidcomponents.

According to still another preferred embodiment said treatment iscarried our during a period of time such that said compressive strengthis at least 60 MPa, in the case of a mineral mixture comprising 95% ofordinary portland cement, 5% of silica fume, and in addition 16% ofwater by the weight of the solid components.

According to the present invention the method for producing cementuseful for ultra high strength and high density concrete comprises thesteps of:

1. Dosage of the solid components;

2. Dry mixing of the solid components;

3. Mechanicochemical treatment of the combined mixture in the millingequipment, preferably in a vibration mill where every particle of themixture receives a large number of direct-changing, randomly distributedimpact pulses.

The dry mixing in said first stage is carried out in such a way that themixture is treated in a highly intensive mixer or in said millingequipment with parameters of treatment adjusted to the mixturecomposition.

According to the present invention the mechanicochemical treatment of acombined mineral-polymeric or mineral mixture of portland cement andSiO₂ -containing microfiller and/or powdery water-reducing agent iscarried out in a media milling equipment (e.g. stirred, centrifugal,tumbling ball and etc.) or a non-media milling equipment (e.g. jet,impact, roller).

Media milling equipment includes mills employing grinding media in theform of balls, cylinders, cylbeps etc., e. g. tumbling ball mills andvibratory mills, or high speed agitators, e.g. stirred mills etc.. Inthis type of mill the treatment of the mixture according to the presentinvention takes place mainly due to the fact that every particle of themixture receives a large number of impact impulses from the grindingmedia in quick succession.

In non-media milling equipment treatment of the mixture takes place dueto subjecting the particles to a high pressure from a moving roller orhammer, e.g. roller or impact mills, or due to mostly particle toparticle impacts or collisions of particles with a target depending onthe design, e.g. fluid energy jet mills, which result in modification ofparticle surface properties.

The preferable equipment is a vibration mill characterized by thediameter of the vibration cycle being, preferably, from 2 to 30 mm andfrequency being, preferably, from 800 to 2000 rpm.

The parameters of treatment in other types of milling equipment shouldbe adjusted to the composition of the mixture subjected to treatment insuch a way that the mechanical treatment corresponds to that obtained ina vibration mill.

According to the present invention the treatment in the millingequipment takes place in a batch regime with the time of treatment,preferably from 3 to 60 min, or continuously, with the feed rateadjusted to the type of the mill and composition of the mixture.

In the case of using a media milling equipment, preferably a vibrationmill, the proportion between the grinding media and the mixturesubjected to treatment, i.e. media to feed ratio, is preferably from 7:1to 15:1 by weight.

The preferred grinding media of the vibration mill is a mixture ofcylbeps, i.e. cylinders with rounded ends made from e.g. aluminum orbodies with an aluminum oxide cover or steel, with equal height and adiameter of 12 and 9 mm, respectively. The proportion between the twoparts is from 2:1 to 1:2 by weight, preferably 1:1 by weight.

The components in the blended cement are present in the followingmaximum limits of weight ranges:

portland cement=98.9%

SiO₂ -containing microfiller=20%

powdery water-reducing agent=3%.

The preferable weight ranges of the components in the blended cementare:

portland cement=89.5-96.7%

SiO₂ -containing microfiller=3-10%

powdery water-reducing agent=0.3-1.5%.

Different types of portland cement, and also in combination with othertypes of cement, can be used according to the present invention.

SiO₂ -containing components are useful as microfillers. They have aparticle diameter which preferably is lower than 1 μm. The microfillercan be silica fume, ground sand, etc., preferably silica fume(microsilica).

The silica fume preferably used in this invention comprises extremelysmall spherical, amorphous particles containing at least 85% by weightof SiO₂. The specific surface area is between 15 and 30 m² /g and theparticles have a diameter between 0.1 and 0.2 μm. Silica fume isnormally obtained from off-gases from electric smelting furnaces usedfor production of silicon and ferrosilicon, but it can also be producedby reduction of SiO₂ to SiO-gas and reoxidation of SiO in air.

Powdery, solid state, water-reduction agents preferably used accordingto the present invention may be water-reducing agents of melamine ornaphthalene type known to be used in ordinary concrete, for example"MIGHTY 100".

According to the present invention the ratio between the specificsurface areas of the mineral components, i.e. cement and SiO₂-containing microfiller, in the mixture preferably is 1:10 to 25. Theratio between the specific surface areas of the mineral part in thecombined mixture, i.e. cement with SiO₂ -containing microfiller, and thepolymeric part, i.e. powdery water-reducing agent, preferably is 1:0.10to 2.0.

According to a preferred embodiment of the present invention differentinorganic materials, e.g. slag, milled sand, metal fibers etc., and/ororganic materials, e.g. polymers, polymer fibers etc., which materialsinfluence the rheological, the mechanical the durability and otherproperties of the fresh and hardened paste, mortar or concrete, areadded to the treated mixture or to the mixture during the treatment.

According to a further preferred embodiment of the invention the abovesaid treatment takes place at a raised or reduced pressure,alternatively in the presence of a protective gas.

A process for preparing a shaped concrete element or structure with theuse of the present invention comprises the following steps:

1. Dosage of the portland cement and SiO₂ -containing microfillersand/or powdery water-reducing agent;

2. Dry mixing of the above mentioned components;

3. Mechanicochemical treatment of the combined mixture in millingequipment according to the specification of the present inventionaccording to the process described above;

4. Mixing the obtained cement with sand and aggregates and water,casting a shaped element or structure and hardening the concrete.

The invention is illustrated by means of the following examples.However, the following examples are not intended to restrict theinvention in any manner.

EXAMPLES

The ordinary portland cement (OPC), produced by Cementa AB Sweden,silica fume produced by Elkem A/S, Norway and powdery water-reducingagent "MIGHTY 100", produced in Japan, were chosen in these experiments.

The mixtures according to the present invention were subjected tomechanicochemical treatment in the first stage by intensive mixing in amixer named "TONIMIX" with a rotation speed of 280 rpm during 3 minutes.The mixer is made by TONI Technik, Germany.

Compositions of the blended cements are presented in Table 1. Theblended cements were subjected to mechanicochemical treatment accordingto the present invention in a vibration mill having a diameter of thevibration circle of 10 mm, operating at a frequency of 1100 rpm during aperiod of treatment of 30 minutes. The proportion between the grindingmedia and mixture was 9:1 by weight.

In the control mixture silica fume and water-reducing agent wereintroduced with water during mixing of the cement paste or concretemixture.

Table 2 presents characteristics of the concrete mixtures obtained withtreatment according to the present invention and untreated cements, i.e.conventional cements.

In concrete mixtures cured at negative temperatures (-10° C. and -20°C.) an antifreezing admixture "BETEC", produced by Finja Betec AB,Sweden, was used.

The cement paste and concrete were tested with the use of cubes with 20mm and 100 mm sides, respectively. A Hobart mixer was used for mixingthe cement paste for 2 minutes. A pan mixer was used for mixing of theconcrete mixture for 3 minutes.

A mercury porosimeter Pore Size -9310 (Micrometers) was used for theexamination of the cement paste porosity.

The temperature effect on the hardening process was studied bymeasurements of strength growth at different hardening temperatures,namely 5°, 20°, 35° and 50° C., respectively. The test samples werecube-shaped bodies having the dimensions 100×100×100 mm and were storedin water.

Liberated heat at hydration of the concrete was calculated frommeasurements of the temperature development during adiabatic andsemi-adiabatic conditions. Each test specimen was about four liters ofconcrete placed in a bucket of thin walled steel.

From the results presented in Tables 1 and 2 and FIGS. 1-4 it can beclearly seen that the strength development and ultimate strength of theconcretes prepared with the use of cement according to the presentinvention are substantially higher in a wide range of curingtemperatures in comparison with the conventional reference concretes.

The cement pastes with treated cements are characterized by a much lowerporosity, as is shown in FIG. 7.

The liberated heat due to hydration per strength unit for concretes withtreated cements is lower than for reference concretes, as is shown inFIG. 6.

There is a wide range of suitable applications for the cement producedaccording to present invention. The applications include concreteelement production, winter concreting, repair of buildings andrehabilitation, roads, floors, topping of concrete, etc.

What is claimed is:
 1. A method for producing cement useful forpreparing pastes, mortars, concretes or other cement-based materials,which method comprises: providing cement particles and at least one of afirst component including an SiO₂ containing microfiller and a secondcomponent including a polymer in the form of a powdery water-reducingagent, mixing the cement and said at least one component intensively ina first treatment stage and in a dry state, whereby particles of the atleast one component are adsorbed on surfaces of the cement particles toproduce a resulting mixture of dry, coated cement particles, impactingthe dry, coated cement particles from the first treatment stage during asecond treatment stage in a milling device in which the coated cementparticles in said mixture receive in quick succession a plurality ofdirect-changed impact impulses for producing shape deformations andmicrodefects in surfaces of the cement particles, resulting inmodification of surface activity properties of the cement particleswhich provide to the cement particles increased surface energy andchemical reactivity so that the cement particles are attracted to eachother to promote consolidation and agglomeration of the particles, andcontinuing said second treatment stage for a sufficient period of timein order that a 1-day compressive strength of a 20 millimeter per sidecube of cement paste, which has been compacted under vibration andhardened at +20° C. in a sealed container is at least equal to 60 MPa.2. A method according to claim 1, wherein the impacting step isperformed in a vibrating milling device, with cylbeps as a vibratingmilling medium, and wherein the milling device has a vibration cyclehaving an amplitude of from 2 to 30 mm and a frequency of vibration offrom 800 to 2000 rpm.
 3. A method according to claim 1, wherein saidcompressive strength is at least 70 MPa for a mineral-polymeric mixturecomprising 94% of ordinary portland cement, 5% of silica fume, 1% of apowdery water-reducing agent, and 16% of water by weight of solidcomponents of the mixture.
 4. A method according to claim 1, whereinsaid compressive strength is at least 65 MPa for a mineral-polymericmixture comprising 99.0% of ordinary portland cement, 1% of a powderywater-reducing agent, and 16% of water by weight of solid components ofthe mixture.
 5. A method according to claim 1, wherein said compressivestrength is at least 60 MPa for a mineral mixture comprising 95.0% ofordinary portland cement, 5% of silica fume, and 16% of water by weightof solid components of the mixture.
 6. A method according to claim 1,wherein the impacting step takes place for a time of from 3 to 60minutes.
 7. A method according to claim 2, wherein milling occurs in amedia mill device and the proportion between grinding media in the milland the mixture subjected to treatment, is from 7:1 to 15:1 by weight.8. A method according to claim 1, wherein the mixture comprises 98.9%portland cement; 20% SiO₂ -containing microfiller and 3% of a polymer inthe form of a powdery water-reducing agent.
 9. A method according toclaim 1, wherein the mixture has a ratio of specific surface areas ofthe cement to SiO₂ -containing microfiller of 1:10 to 1:25 and a ratioof specific surface areas of the coated cement particles to the powderywater-reducing agent, of 1:0.1 to 1:2.0.
 10. A method according to claim1, wherein the powdery water-reducing agent is a melamine-containingreducing agent and the SiO₂ -containing microfiller is silica fume. 11.A method according to claim 1, further comprising the step of addinginorganic materials selected from the group consisting of slag, milledsand, and metal fibers to the mixture during the mixing step.
 12. Amethod according to claim 1, wherein mixing takes place at an elevatedpressure.
 13. A process for preparing a shaped concrete element orstructure which comprises the steps of producing a cement according tothe method of claim 1, mixing said cement with water and one of fineaggregate or coarse aggregate, casting a shaped element and hardeningthe shaped element.
 14. A method for producing cement useful forpreparing pastes, mortars, concretes or other cement-based materials,which method comprises: preparing a cement-based composition inaccordance with claim 1 and adding the cement-based composition to aportland cement composition.
 15. A method according to claim 1, whereinthe milling step takes place continuously.
 16. A method according toclaim 1, wherein the powdery water-reducing agent is anaphthalene-containing water-reducing agent and the SiO₂ -containingmicrofiller is silica fume.
 17. A method according to claim 1, furthercomprising the step of adding organic materials comprising polymers orpolymer fibers to the mixture during the mixing step.
 18. A methodaccording to claim 1, wherein mixing takes place at a reduced pressure.19. A method according to claim 12, wherein mixing takes place in thepresence of gas.
 20. A method according to claim 18, wherein mixingtakes place in the presence of gas.